1. Field of the Invention
The present invention relates to a radio wave receiver.
2. Description of the Related Art
As one of radio wave receivers, there has conventionally been known a radio-controlled timepiece which includes a case body (device body) and an antenna to receive a standard radio wave (standard time and frequency signal) containing time data inside the case body, wherein the time is corrected based upon the standard radio wave received by the antenna.
The radio-controlled timepiece described above includes the one described below. Specifically, in order to achieve a high-quality appearance, the case body and a rear case as a closing member are made of a metal, and screw portions are formed on an inner peripheral wall surface of the case body and an outer peripheral wall surface of the rear case, wherein screw portions are engaged with each other so as to screw the case body and the rear case.
However, when the metallic case body and the metallic rear case are electrically conductive in the radio-controlled timepiece described above, an electric current circulating in the case body and the rear case increases, entailing a problem of a significant deterioration in the receiving sensitivity of the antenna.
In order to solve such problem, a radio-controlled timepiece described below has been proposed (for example, see Japanese Patent Application Laid-Open Publication No. 2008-76326). This radio-controlled timepiece has, inside the case body, an inner extending portion and a casing frame which is in contact with the inner extending portion through an insulating member. A screw portion on the rear case is screwed to a screw portion formed on the casing frame, whereby the case body and the rear case are electrically insulated.
There has also been proposed a radio-controlled timepiece as described below (e.g., see Japanese Patent Application Laid-Open Publication No. 2007-263572). In the radio-controlled timepiece, cutouts are formed in spots on a metallic projecting portion of the rear case, on which projecting portion a screw portion is formed, whereby the screw portion is divided by the cutouts. This decreases an area where the screw portion on the rear case and the screw portion on the case body screw together, so as to reduce the total area of the case body and the rear case, whereby the deterioration in the receiving sensitivity can be prevented.
However, the radio-controlled timepiece described in Japanese Patent Application Laid-Open Publication No. 2008-76326 employs the casing frame which is separately provided from the case body and the rear case, which might entail a problem of complicated attaching operation of the rear case to the case body. Moreover, since the radio-controlled timepiece has the casing frame inside the case body, the case body has to be enlarged.
Meanwhile, in the radio-controlled timepiece described in Japanese Patent Application Laid-Open Publication No. 2007-263572, though the area where the screw portions screw together can be decreased, since the screw portion on the rear case and the screw portion on the case body are in metallic contact, the electrical insulation between the case body and the rear case cannot surely be established. Further, since the cutouts are formed on the projecting portion on which the screw portion is formed, a coupling force between the case body and the rear case is decreased by the cutouts.